The present invention relates to a servo-valve arrangement with high pressure and low pressure connections and two parallel throttle sections leading from the high pressure side and which is provided to the low pressure side with series-connected controllable throttling places on the high-pressure and low-pressure side. Two separate motor connections branches off from the throttle sections each between the high-pressure and low-pressure sides thereof for the connection of input and outlet lines of a servo-motor. A control piston simultaneously controlls the throttling places which, for purposes of producing a controllable pressure difference between the motor connections, increases the resistance of the high pressure side throttling place with an adjustment as well as reduces the resistance of the low pressure side throttling place, while simultaneously reducing at the other throttling place the resistance of the high pressure side throttling place as well as increasing the resistance of the low pressure side throttling place. Two piston working spaces are coordinated to separate operating surfaces of the control piston which, upon actuation with different pressures, permit the production of a force opposing the respective displacement of the piston. A third throttle section having a throttling place and a controllable throttle for changing the actuating forces of the servo-valve arrangement in dependence on control magnitudes.
A servo-valve arrangement of this type is described in the DE-OS 36 25 003. In this prior art arrangement, the end faces of the control piston are arranged in separate chambers which are each connected by way of a check valve opening in the direction of the chamber with one of the motor connections, respectively, with spaces connected therewith. The two chambers are connected with each other by way of a line which is connected between two series-connected throttling places with a throttle valve arrangement leading to a pressureless reservoir. This throttle valve arrangement is controlled in dependence on the driving velocity of a vehicle as well as in dependence on the system pressure. A more or less large pressure difference will thereby establish itself between the chambers depending on the throttling resistance of the throttle valve arrangement when the control piston establishes differing Pressures at the motor connections by a corresponding displacement. As a result thereof, the actuating forces of the servo-valve arrangement can be changed in order to prevent that the servo-valve arrangement will be overcontrolled unintentionally.
It is the object of the present invention to provide a servo-valve arrangement in which the forces acting back on the control piston can be varied in very different ways combined with low constructive expenditures.
The underlying problems are solved according to the present invention in that the one piston working space is arranged on the one side of the one throttling place and the other piston working space on the other side of the one throttling place which is arranged as part of the third throttle section between the motor connections or the piston working spaces connected therewith in series with further controllable throttles which are controllable in dependence on external control magnitudes and pressure differences occurring at the third throttling place.
The present invention is based on the recognition that it suffices to arrange between the motor connections a series of controllable throttling places and to act upon the piston working spaces with different pressures corresponding to the pressure drop at one throttling place. Notwithstanding this simple arrangement, a very flexible working behavior of the servo-valve arrangement can be achieved.
According to a preferred embodiment of the present invention, provision is made that the one of the controllable throttles in the third throttle section is an externally controllable throttle and the other is a throttle controllable by the pressure drop at the throttling place between the piston working spaces. On the basis of this construction of the servo-valve arrangement, a servo-control can be attained with a variable proportional range and a constant limitation of the actuating force.
In a second preferred embodiment of the present invention, provision is made that the one of the controllable throttles in the third throttling section is an externally controllable throttle and the other is a throttle adjustable by the pressure drop at the externally controllable throttle. With this construction of the servo-valve arrangement, a servo-control with a variable proportional range and a variable limitation of the actuating force can be created.
Therebeyond, it may also be appropriate to additionally arrange within the third throttle section a throttle controllable by the pressure difference between the motor connections. A servo-control with a variable proportional range having two ranges of different proportionality and a constant limitation of the actuating force can be achieved therewith.
In a constructively particularly preferred embodiment of the present invention, provision is made for piston working spaces to be arranged at end-face of the control piston. The control piston is traversed by a longitudinal bore and a further piston is slidingly displaceably guided in the longitudinal bore of the control piston against a spring force from its normal position in opposite directions. The further piston is traversed by a further longitudinal bore with a throttling place. The control piston and the further piston have mutually overlapping radial openings which form a throttling resistance dependent on the relative displacement between the control piston and the further piston and connect with a space connected with one motor connection as well as the further longitudinal bore of the further piston on one side of the throttling place arranged therein. The piston working space located on the other side of this throttling place being arranged in the further piston and communicates by way of the externally controllable throttle with the other motor connection, respectively, with a space connected therewith.
With this arrangement, all throttling places of the third throttle section with the exception of the externally controllable throttle, are arranged inside of the control piston so that a particularly simple construction is attained, for essentially only the further piston must be displaceably arranged inside of the control piston against spring force.